Commercial scale hydrogenation of functionalized aromatics, such as methylenedianiline, is typically carried out using slurry catalysts. The resulting methylene di(4-aminocyclohexane) has to be separated by filtration from the slurry catalyst after the completion of the hydrogenation. The product/catalyst separation step adds significantly to the production cycle time and to the cost of manufacture due to the high cost of recycling precious metal catalysts.
Slurry catalysts present problems in industrial processes due to the inherent recovery problems. These catalysts are recovered from the reaction product by filtration means. Such filters often become plugged. In addition, some of the catalyst is lost in the filtration step.
The following patents are provided to illustrate various process for the ring hydrogenation of methylenedianiline using slurry catalysts:
U.S. Pat. Nos. 2,511,028; 2,606,924; 2,606,925; and 2,606,928 disclose a general process to hydrogenate methylenedianiline(MDA) to bis(para-aminocyclohexyl)methane (PACM) using a supported ruthenium catalyst under pressures in excess of 200 psig (1480 kPa), preferably in excess of 1,000 psig (6996 kPa), at temperatures within a range of 800 to 275° C. The hydrogenation is carried out under slurry conditions with an inert organic solvent. Under these conditions, the reaction rate is generally slow and a substantial amount of byproducts, such as PACM secondary amines, are formed.
U.S. Pat. Nos. 3,636,108; 3,644,522; 3,697,449 and 4,448,995 teach the base modification of supported ruthenium catalysts with alkali metal and alkaline earth metal salts, including hydroxides, nitrates and sulfates, in the hydrogenation of methylenedianiline to reduce the formation of byproducts.
U.S. Pat. Nos. 3,591,635 and 3,856,862 disclose the use of supported rhodium, as a catalytic metal instead of ruthenium, as a catalyst for MDA hydrogenation to PACM. The rhodium catalyst is base moderated using either ammonium hydroxide as a pretreatment or ammonia in situ. Good hydrogenation rates are achieved with rhodium catalysts in general.
U.S. Pat. No. 4,754,070 describes a catalyst system for the ring hydrogenation of crude methylenedianiline employing ruthenium and rhodium alumina supported catalysts resulting in good hydrogenation rate.
U.S. Pat. No. 5,196,587 discloses a process for the catalytic hydrogenation of crude methylenedianiline using a catalytic pretreatment of the crude methylenedianiline. The process comprises passing the crude feedstock over a ruthenium catalyst carried on an alumina support, cooling, venting hydrogen, filtering, and then hydrogenating the pretreated crude feedstock over a ruthenium/rhodium catalyst.
U.S. Pat. No. 6,184,416 teaches the ring hydrogenation of methylenedianiline using a rhodium catalyst carried on a lithium aluminate support. The inert support allows more effective base modification, which results in better selectivity and higher PACM yield.
U.S. Pat. No. 6,506,361 discloses the use of a monolith reactor in combination with an ejector to effect hydrogenation of organic compounds.